Feral pigs, vampire bats, and infectious diseases in rural Brazil

The distribution of feral pigs — which are also known as wild boars, or “javali” in Portuguese, and are actually the same species as the domestic pig (Sus scrofa) — has increased five-fold since they were first recorded in Brazil in 2007.

A group of Brazilian researchers found that not only might vampire bat populations explode as a result of this invasion of feral pigs, but associated threats, such as the spread of infectious diseases, could increase as well.

Wild boar are becoming a dominant mammal in Brazil’s Atlantic forest and could potentially invade the Amazon region.

A new study examines the impacts of invasive feral pigs, a favorite prey of vampire bats, on ecosystems in rural Brazil.

The distribution of feral pigs — which are also known as wild boars, or “javali” in Portuguese, and are actually the same species as the domestic pig (Sus scrofa) — has increased five-fold since they were first recorded in Brazil in 2007.

A group of Brazilian researchers found that not only might populations of vampire bats (Desmodus rotundus) explode as a result of this invasion of feral pigs, but associated threats, such as the spread of infectious diseases, could increase as well. The results of their study were published in the journal Frontiers in Ecology and the Environment earlier this month.

The wild boar is becoming a dominant mammal in Brazil’s Atlantic forest and could potentially invade the Amazon region, as well, according to Felipe Pedrosa, an ecologist from São Paulo State University in Brazil who studies the impacts of feral pigs on biodiversity and co-authored the study.

The natural range of Sus scrofa is mostly in Europe and Asia, but the species, which is considered one of the worst invasive species in the world, has been introduced in Australia, South America, and the USA. As wild boars invade new territory, damage to crops such as maize, sugarcane, and soybeans as well as predation of native birds and mammals usually increases as well. The study notes that this trend has been shown in all ecosystems invaded by wild boars, from Australia to Hawaii and Texas.

But the researchers discovered the potential for an unprecedented effect that could occur in Brazil. As their numbers increase, feral pigs provide an ever-increasing blood supply to vampire bats, increasing the bat’s population in turn. Vampire bats are a threat to livestock and humans alike throughout the tropical Americas due to their role as a “reservoir” of several infectious diseases, including rabies, the researchers say.

Incidence of rabies among vampire bats is about three for every two hundred individuals, or 1.4 percent of vampire bat populations. Because the species is relatively rare in the wild, and cattle and dog vaccination programs are practiced intensively in Brazil, the chances of humans contracting rabies are relatively low — but the researchers say their observations have led them to believe there is a significant chance of an increase in human rabies cases nonetheless, in addition to increased transmission of disease to other wildlife.

As part of the study, Mauro Galetti, a professor of ecology at São Paulo State University in Brazil and the study’s lead author, led the team of researchers in monitoring wildlife using camera traps across a wide range of rural sites in both the Atlantic forest and the Pantanal, a tropical wetlands located primarily in the western Brazilian state of Mato Grosso do Sul.

“During analyses of more than 10,000 photos and videos, we noticed some vampire bats feeding on wild boars, tapir and deer. Our initial impression was that the feeding events were rare, but after calculating the probability of the animals being attacked by a bat, we were shocked,” Galetti said in a statement.

Galetti and team found that the number of encounters between vampire bats and wild boars was especially high, about 10 percent of all night-time animal records. The researchers warn that this could lead to a potential increase in rabies outbreaks among wildlife, non-vaccinated livestock and domestic animals, and rural people as the wild boar and vampire bat populations continue to increase.

It’s not just rabies that is a cause for concern, either. “For native animals that are bitten by vampire bats, like tapir and deer from our video records, there is also the potential for transmission of other viral diseases carried by feral pigs,“ Alexine Keuroghlian, a conservation biologist with Wildlife Conservation Society – Brazil, said in a statement.

Poorly defined policies for control of invasive species in Brazil will all but ensure that wild boar populations will continue to expand, Galetti and team say. In response, populations of native vampire bats are also likely to increase. Given that the wild boar invasion in rural Brazil poses a serious threat to native wildlife and human health, there is an urgent need to develop and implement effective control measures, the researchers added.

One potential solution is to control the feral pig population by legalized hunting, but Galetti and team are skeptical, arguing that this measure could heap even more harm on native wildlife. “Our major challenge is to allow the control of feral pigs without indirectly incentivizing illegal hunting on native wildlife,” Galetti said.